Aside from the places where I have corrected it, I think that your grammar, for the most part, is fine. However, I did reword some sections and add some words (my additions are in brackets below) to make it either more grammatical or else simply to flow better. There are a few parts that are not altogether clear (eg, what is a “well-thinking skill”?) and you may want to revise these as well. You can send me another draft if you like
English is [quite] hard [f]or me especially in writing.
[Recently], English has become a global language [and is increasingly used for communication in a broad variety of fields]. As we can see [,]almost every field in Thailand [,including] education, business, medicine, and even entertainment are all related to English. Consequently, [learning how to use the] English language effectively is very important to Thai people. Therefore, almost all [of the] schools in Thailand [must] include English [as a] subject in the curriculum from grade 1 [onwards]. [This] means [that] Thai students are required to study English [for] at least nine years. [However], despite the fact that they have studied English for several years, [most] Thai people cannot communicate fluently in English.
The first reason for this is the limited time devoted to English in Thai schools (about 3-5 hours [of] English class per week). Consequently, children do not have much time to learn and practice English. As we all know, it is [impossible] to add more English class hours into the Thai schools’ curriculum because they are already overloaded. The solution to this problem might [be] to adjust the curriculum [so that students are forced] to study in English program[s] at [an] early age[,] like in international schools. This method might help students [start] learning and using English more effectively.
Another significant reason students cannot communicate in English is [that] they do not have a well-thinking skill which leads them to face a hard situation in speaking [when they are] afraid of making mistakes and los[ing] face in public. I believe in the saying that “We cannot think unless we have memories”. In order to improve students’ thinking skill[s] [and increase their efficiency in English], they [will need] to memorize many grammatical rules, [a large vocabulary] and numerous idiomatic expressions. When they are able to manage these, they will be able to think [systematically] and be able to speak fluently.
In conclusion, for [the] two reasons mentioned above, students are not able to improve their English skills [effectively]. Students must have a strong will in learning and practicing a lot of English. Besides learning in a classroom, [this] can be done in several ways. [For example, effective practice techniques can include] listening to English news channels such as BBC and CNN, learning from online English lesson[s] on the internet, reading English newspapers and so on. Once they are good at English, they must keep learning and practicing it, otherwise they will forget what they have learned.